Over the years various sealing arrangements have been designed for rotatable shafts which extend into a fluid holding tank through a side opening below the fluid surface. The drive unit used for driving the rotary shafts are typically located outside the tank so that arrangements must be made for sealing the tank at the point of shaft entry. Packing and mechanical seals (e.g. rotary seals) for such purposes are well-known, but they are subject to wear and must be replaced from time-to-time.
Typically, when the worn packing or components of a mechanical seal need replacement, the contents of the tank must be drained or otherwise removed to prevent fluid escape from the shaft opening during the servicing operation. The emptying of the tank is a time-consuming and expensive process. Also it can potentially cause undesirable waste of some or all of the contents of the tank as well as contamination of the tank contents. In some applications, it can even expose the operators to potentially harmful substances.
U.S. Pat. No. 2,911,240 issued on Nov. 3, 1959 addresses the above issues by mounting an auxiliary sealing member inside the tank on an inboard end of a two-part rotary shaft. The shaft opening in the tank is temporarily sealed during servicing by moving the rotary shaft axially away from the tank to bring the auxiliary sealing member in sealing contact with a mating seal seat provided inside the tank. The auxiliary sealing member and the mating seat are exposed to the tank contents at all time. In some applications, the tank contents may compromise the operation of the auxiliary seal. This is particularly problematic in scaling environments where the build-up of material deposits on the sealing surfaces may prevent proper sealing engagement thereof.
Accordingly, there is a need to provide an improved sealing arrangement which addresses the above mentioned issues.